The goal of this proposal is to understand the molecular basis for vertebrate neural patterning, using the frog Xenopus. Focus will be on the role of the zinc finger gene opl, which was isolated by subtractive cloning in the Sive lab and is one of the earliest known neural markers. Opl is a homologue of the Drosophila pair-rule gene opa which regulates the expression of wingless and engrailed and it is a member of the vertebrate Zic gene family. In mid-gastrula, opl is expressed throughout the prospective neurectoderm with subsequent restriction to the dorsal neural tube and neural crest. Opl can activate expression of the dorsal neural marker pax3, and the midbrain-specific marker engrailed (en-2), suggesting that opl is a regulator of neural patterning. This raises the question of how a single gene can activate genes in different parts of the neural tube. I will address the mechanisms by which this distinction might be made, and the normal role of opl in neural determination. I have shown that opl acts through the Wnt pathway to induce en-2, making opl a strong candidate for an activator of Wnt proteins in vertebrates. In this proposal I will first ask whether induction of pax3 expression by opl also requires Wnt signalling. If it does, candidate Xwnts that may be mediators of pax3 activation will be identified. otx2 is a potential co-regulator of opl and may be involved in activating en-2 expression and preventing pax3 expression in the anterior of the embryo, which will be tested using an animal cap assay. The in vivo activity of opl will be examined using a misexpression assay in whole embryos and by constructing dominant interfering Opl proteins. Together, these approaches will give insight into the function of opl and the mechanism by which it reuglate neural patterning. Since human homologues of opl are highly conserved, these studies will add to our understanding of genes that regulate normal neural tube formation and will suggest mechanisms by which neural tube birth defects may occur.